Search Results (2 total)

Advanced high-brightness beam applications such as inverse-Compton scattering (ICS) depend on achieving of ultrasmall spot sizes in high current beams. Modern injectors and compressors enable the production of high-brightness beams having needed short bunch lengths and small emittances. Along with these beam properties comes the need to produce tighter foci, using stronger, shorter focal length optics. An approach to creating such strong focusing systems using high-field, small-bore permanent-magnet quadrupoles (PMQs) is reported here. A final-focus system employing three PMQs, each composed of 16 neodymium iron boride sectors in a Halbach geometry has been installed in the PLEIADES ICS experiment. The field gradient in these PMQs is 560   T/m, the highest ever reported in a magnetic optics system. As the magnets are of a fixed field strength, the focusing system is tuned by adjusting the position of the three magnets along the beam line axis, in analogy to familiar camera optics. This paper discusses the details of the focusing system, simulation, design, fabrication, and experimental procedure in creating ultrasmall beams at PLEIADES.

Velocity bunching has been recently proposed as a tool for compressing electron beam pulses in modern high brightness photoinjector sources. This tool is familiar from earlier schemes implemented for bunching dc electron sources, but presents peculiar challenges when applied to high current, low emittance beams from photoinjectors. The main difficulty foreseen is control of emittance oscillations in the beam in this scheme, which can be naturally considered as an extension of the emittance compensation process at moderate energies. This paper presents two scenarios in which velocity bunching, combined with emittance control, is to play a role in nascent projects. The first is termed ballistic bunching, where the changing of relative particle velocities and positions occur in distinct regions, a short high gradient linac, and a drift length. This scenario is discussed in the context of the proposed ORION photoinjector. Simulations are used to explore the relationship between the degree of bunching, and the emittance compensation process. Experimental measurements performed at the UCLA Neptune Laboratory of the surprisingly robust bunching process, as well as accompanying deleterious transverse effects, are presented. An unanticipated mechanism for emittance growth in bends for highly momentum chirped beam was identified and studied in these experiments. The second scenario may be designated as phase space rotation, and corresponds closely to the recent proposal of Ferrario and Serafini. Its implementation for the compression of the electron beam pulse length in the PLEIADES inverse Compton scattering (ICS) experiment at LLNL is discussed. It is shown in simulations that optimum compression may be obtained by manipulation of the phases in low gradient traveling wave accelerator sections. Measurements of the bunching and emittance control achieved in such an implementation at PLEIADES, as well as aspects of the use of velocity-bunched beam directly in ICS experiments, are presented.